Manufacture of organic polysulphides



Patented July 27, 1943 MANUFACTURE OF ORGANIC POLYSULPHIDES John F. Olinand Thomas E. Deger, Grosse lle,

Mich.

assignors to Sharples Chemicals Inc., a corporation of Delaware NoDrawing. Application March 6, 1941,

Serial No. 381,972

9 Claims.

The present invention pertains to oxidation of organic compounds havingan SM radical, M designating an ammonium or substituted ammoniumradical, a metal or hydrogen. The invention was developed primarily as aprocess for obtaining tetra alkyl thiuram disulphides by oxidation ofsalts of dialkyl dithiocarbamic acids and it will accordingly bedescribed first with particular reference to that problem.

A fairly satisfactory method of manufacturing compounds of this type hasbeen to oxidize salts of dialkyl dithiocarbamic acids with the aid ofammonium persulphate. An object of the present invention has been toproduce these compounds by a more economical process providing excellentyields and conversions, thereby effecting considerable economies ascompared to the prior art ammonium persulphate oxidation meth od.

In an article in the Canadian Journal of Research, volume 2, pages144-52 (1930), Cambron and Whitby have described a process by which asalt of diethyl dithiocarbamic acid is oxidized with a nitrous acid saltat C. by addition of a dilute mineral acid to produce the desired tetraethyl thiuram disulphide, in accordance with the following equation:

2(C2H5)rNCSSNa+2NaNOz+4HCl Cambron and Whitby discussed this reaction onpage 151 of their article, describing an experiment involving treatmentof a mixture containing 45 grams of the sodium salt of diethyldithiocarbamic acid and 18 grams of sodium nitrite in 100 cc. of waterwith 80 cc. of a hydrochloric acid solution. They noted the fact thatthe crystallized tetra alkyl thiuram disulphide obtained by this processhad a melting point of 71 C. and was a relatively pure product, but madeno comment with respect to the conversion or yield obtained in thepractice of the process.

Experiments made by the present applicants have demonstrated thatneither the yield nor conversion obtained in the practice of the Cambronand Whitby process is sufliciently high to warrant commercial adoptionof the process in place of the ammonium persulphate oxidation processdiscussed above.

The present invention rests upon the discovery that excellent yields andconversions may be obtained in the practice of the process described byCambron and Whitby provided a lower aliphatic alcohol is maintained insubstantial quantity in the reaction mixture during the oxidationreaction, or provided a lower alkyl nitrite is substituted for thesodium nitrite which acts as the oxidizing agent.

In the practice of the present invention. methyl, ethyl, propyl,isopropyl, butyl, or a higher alcohol may be mixed with a nitrous acidsalt and the salt of the dialkyl dithiocarbamic acid to be oxidized, andthe resulting mixture may be cooled to a temperature between 20 C. and20 C. while a dilute solution of a mineral acid (e. 8., sulphuric,hydrochloric or phosphoric acid) is gradually added. It is believed thatthe reaction proceeds through two stages, the nitrous acid salt beingfirst converted into the corresponding alkyl nitrite, and this al ylnitrite thereafter serving as the oxidizing agent, as illustrated by thefollowing equations:

As indicated by the above equations, it is preferable to add an amountof alcohol which is at least a molecular equivalent of the quantity ofthe compound to be oxidized, although smaller amounts of alcohol may beused, with somewhat less satisfactory results.

The hypothesis that the reaction proceeds through the initial formationof an alkyl nitrite is substantiated by the fact that experiments havebeen made involving initial production of the alkyl nitrite by reactionof the alcohol with the nitrous acid salt, followed by use of theresulting crude nitrous acid ester-containing reaction' mixture as theoxidizing agent in the above reaction.

While we believe that the reaction proceeds as discussed above, we donot wish to be limited by any theory as to the reasons for the resultsachieved. It may be that the presence of the alcohol, or of the alkylradical of the alkyl nitrite, assists in the oxidation function of thenitrous acid radical by reason of the fact that we obtain anintermediate alkyl ester of the alkyl dithiocarbamic acid, and that thisalkyl ester is more easily oxidized than the corresponding salts.Regardless of theory, however, and regardless of whether an alcohol isseparately added or an alkyl nitrite used, the oxidation reactionmixture will contain both the nitrous acid ester and the aliphaticalcohol after the mineral acid is added.

The following examples provide illustrations of the practice of theinvention in the manufacture of tetra-alkyl thiuram disulphides.

Example I To a cooled solution of 180 grams of 50% caustic in 850 cc.water is added 146 grams diethylamine in cc. water. grams carbondisulphide are slowly added with stirring at,4-7 C. After thepreparation of the sodium diet'nyl dithiocarbamate solution by the abovemethod,

350 cc. water, 152 grams sodium nitrite and 112 grams methanol are addedto the resulting crude reaction mixture. A solution of 495 grams of 37%hydrochloric acid in 400 cc. water is then slowly added with stirring at27 C. The tetraethyl thiuram disulphide precipitates out as a whitepowder and may be filtered oif and washed with water. The productrequires no further treatment than drying. A yield of 90-95% is obtainedof material melting between 68 and 72 0., this material beingessentially tetraethyl thiuram disulphide.

Example II To a cooled solution of 180 grams of 50% caustic soda in 600cc. water is added 361 grams of 25% dimethylamine in 200 cc. water. 160grams carbon disulphide are slowly added with stirring at 4-7 C. Afterthe preparation of the sodium dimethyl dithiocarbamate by the abovemethod, 400 cc. water, 152 grams sodium nitrite and 112 grams methanolare added. A solution of 495 grams 37% hydrochloric acid in 400 cc.water is slowly added with stirring at 1-7 C. The tetramethyl thiuramdisulphide is filtered off, washed with water and dried. It is a white,

crystalline powder, melting between 136 and 138 C. and obtained in 98%yield.

Example III To a cooled solution of 270 grams of 50% caustic soda in1250 cc. water is added 387 grams dibutylamine. 235.6 grams carbondisulphide are then slowly added with stirring at 49 C. To this sodiumdibutyl dithiocarbamate solution is added 224.5 grams sodium nitrite and160 grams methanol. A solution of 666 grams 37% hydrochloric acid in 500cc. water is then slowly added at 2-8 C. The tetrabutyl thiuramdisulphide separates as a yellow oil which is extracted with naphtha,washed with water and vacuum distilled to remove the naphtha. It isobtained in quantitive yields.

Example IV To a cooled solution of 0.30 gram mol. sodium di-isopropyldithiocarbamate in 175 cc. water is added 22.1 grams sodium nitrite and12.8 grams methanol. A solution of 51.8 cc. 37% hydrochloric acid in 48cc. water is slowly added with stirring at 3-7 C. Th solid tetraisopropyl thiuram disulphide is filtered off and washed with water. 34.2grams of product melting between 80 and 90 C. is obtained.

Example V To a cooled solution of 0.30 gram mol. sodium diethyldithiocarbamate in 150 cc. water 3 aMed 22.1' grams sodium nitrite and19.4 grams ethanol. A solution of 51.8 cc. of 37% hydrochloric acid in48 cc. water is slowly added with stirring at 4-7 C. The tetraethylthiuram disulphide is obtained in 95% yield having a melting pointbetween 69 and 72 C.

Example VI The same procedure was followed as in Example V except that24.1 grams isopropanol were substituted for the ethanol. The tetraethylthiuram disulphide was obtained in 90% yield and had a melting pointbetween 69 and 70.5 C.

Example VII To 67.5 grams sodium diethyl dithiocarbamate in 250 cc.water is added 22.4 grams sodium nitrite and 16 grams methanol. Asolution of 17.6 cc. 95.5% sulphuric acid in cc. water is slowly addedwith stirring at 48 C. A 92% yield of tetraethyl thiuram disulphide isobtained melting between 68.5 and 71 C.

Example VIII 23 grams carbon disulphide were slowly added with stirringto a cooled solution of 12 grams sodium hydroxide, 22 grams diethylamineand cc. water. To the sodium diethyl dithiocarbamate thus formed wereadded 22 grams sodium nitrite and 31 grams normal butyl carbinol. Asolution of 51.5 cc. 37% hydrochloric acid and 48 cc. water are thenslowly added at 1 to 8 over a period of 1.75 hours. The unreactedalcohol and possibly some of the amyl nitrite was removed from theprecipitated tetraethyl thiuram disulphide by treatment of the mixtureunder vacuum with a slow stream of air. The solid was then filtered andwashed with water. 18 grams tetraethyl thiuram disulphide of excellentpurity were obtained, melting 70-715.

Example IX *solid. 598 grams or 90.4% yield of the thiuram disulphidemelting at 54 to 58 are obtained.

While the invention has been described above with reference to thespecific problem of oxidizing salts of dialkyl dithiocarbamic acids toproduce tetra alkyl thiuram disulphides, it is applicable to theoxidation of all of the many compounds having an SM radical as discussedabove, including aliphatic, cycloaliphatic, aromatic and heterocycliccompounds. The following are a few examples of such compozmds:

1. Dithiocarbamic acid salts to produce thiuram disulphides.

2. Xanthates to produce xanthogen disulphides.

3. Mono-, di-, and tri-thiocarbonic acids to produce the correspondingdithiocarbonic acid, di-dithiocarbonic acid and di-tri-thiocarbonicacid, respectively.

4. Mercaptans and mercaptides to produce disulphides.

In the practice of the invention in oxidizing organic acids, such as thethiocarbamic and thiocarbonic acids, we prefer to treat these acids inthe form of their alkali metal or ammonium salts, since improved yieldsare obtained by treating the salts instead of the free acids; i. e.,oxidizing the acids in their nascent state as they are liberated fromtheir salts. In oxidation of mercaptans, on the other hand, there is noparticular advantage in converting the mercaptans into mercaptidesbefore oxidizing them.

The following example will illustrate the practice of the invention asapplied to the oxidation of mercaptobenzothiazole to producebenzothiazyl disulphide, according to the following equation:

2RoH+2Nac1+2No+2mo Ewample X 50.1 grams (0.30 gram mol.)mercaptobenzothiazole, 22.1 grams (0.32 gram mol.) sodium nitrite, 600cc. water and 19.2 grams (0.60 gram mol.) methanol are charged into aflask equipped with thermometer well, mechanical stirrer and droppingfunnel. A solution of 26.8 cc. (0.323 gram mol.) of 37% hydrochloricacid in 100 cc. water is slowly added at 2-5 C. with vigorous stirring.The precipitate which is now benzothiazyl disulphide is filtered off anddried in a current of air at 50-70 C. The yield is practicallyquantitative.

The following examples also illustrate the practice of the invention asapplied to the oxidation of sulphur-containing organic compounds.

Example XI To a cooled solution of 56 grams sodium amyl xanthate (sodiumamyl sulphothiocarbonate), 22 grams sodium nitrite and 15 grams ethanolin 200 cc. water were added with stirring a solution of 52 cc. 22 Baumhydrochloric acid in 50 cc. water over a period of 1.5 hours whileholding the temperature below 5 C. After reaction the oil layer wasextracted with ether, washed with water and dried under vacuum on awater bath. 32 grams amyl xanthogen disulphide were obtained as a deepyellow slightly viscous oil.

Example XII To a stirred, cooled mixture of 37 grams benzyl mercaptan 12grams sodium hydroxide, 22 grams sodium nitrite, 15 grams ethanol and200 cc. water was slowly added a solution of 52 cc. 37% hydrochloricacid in 50 cc. water in 1.5 hours at 3 to 7 C. A red oil layer settledout which on slowly warming to 35 was decomposed to benzyl disulphidewith the evolution of nitrogen oxides. 35 grams of white, crystallinebenzyl disulphide were obtained which melted at 67-68 C.

Example XIII To show that the metallic salt was not necessary in theoxidation of a mercaptan by the alkyl nitrite process the above ExampleXII was repeated with the exclusion of the sodium hydroxide. About thesame results were obtained. 31.5 grams white benzyl disulphide melting6'7-63 C. were produced.

Somewhat higher temperatures may be employed in the treatment ofmercaptans and mercaptides than in the treatment of thio-acids. Thetemperature range depends on the stability of the compounds treated,higher temperatures being permissible'in treatment of the more stablecompounds. In general, we prefer to maintain thio-acids and their saltsat temperatures between and +20 C., and mercaptans and mercaptidesbetween 5 and 35 C., during the oxidation reaction.

As indicated by the above examples, we prefer to maintain a considerablequantity of water in the reaction mixture, although the presence ofwater is not a necessity. The most important advantage of having waterpresent is that the oxidation products of the reaction are usuallysoluble in water and may therefore be separated as aqueous solutionsfrom undesired lay-products .by simple decantation.

A number of modifications will be evident to those skilled in the artand we do not therefore wish to be limited except by the scope of thefollowing claims.

We claim:

1. In the manufacture of organic polysulphides, the process comprisingoxidizing an organic compound containing an SM radical, in which Sdesignates sulphur and M designates a. member chosen from the groupconsisting of ammonium and substituted ammonium radicals, metals andhydrogen, which comprises mixing said compound with a mineral acid inthe presence of an alkyl nitrite.

2. In the manufacture of organic polysulphides, the process comprisingoxidizing an organic compound containing an SM radical, in which Sdesignates sulphur and M designates a member chosen from the groupconsisting of ammonium and substituted ammonium radicals, metals andhydrogen, which comprises mixing said compound with a mineral acid inthe presence of a nitrous acid salt and an aliphatic alcohol.

3. In the manufacture of organic polysulphides, the process comprisingoxidizing an organic compound chosen from the class consisting ofmercaptans and mercaptides by mixing the compound to be oxidized with amineral acid in the presence of an alkyl nitrite.

4. In the manufacture of organic polysulphides,

the process comprising oxidizing an organic compound chosen from theclass consisting of mercaptans and mercaptides by mixing the compound tobe oxidized with a mineral acid in the presence of a nitrous acid saltand an aliphatic alcohol.

5. In the manufacture of organic polysulphides, the process comprisingoxidizing an organic compound chosen from the class consisting oforganic thio-acids and salts thereof by mixing the compound to beoxidized with a mineral acid in the presence of an alkyl nitrite.

6. In the manufacture of organic polysulphides, the process comprisingoxidizing an organic compound chosen from the class consisting oforganic thio-acids and salts thereof by mixing the compound to beoxidized with a mineral acid in the presence of a nitrous acid salt andan aliphatic alcohol.

7. A process as defined in claim 3 in which the temperature of thereaction mixture is maintained between 5 and 35 C. during the oxidationreaction.

8. A process as defined in claim 5 in-which the temperature of thereaction mixture is maintained between 20 C. and -20 C. during theoxidation reaction.

9. A process as defined in claim 1, in which water is also maintained inthe reaction mixture.

JOHN F. OLIN. THOMAS E. DEGER.

